1. Field of the Invention
The present invention is related to an optical sensor, and more particularly, to an optical sensor capable of detecting IR light and visible light simultaneously.
2. Description of the Prior Art
Light is the portion of electromagnetic radiation whose wavelength is between 300 nm (ultraviolet) to 14,000 nm (far infrared). The wavelength of visible light lies in a range from about 380 to about 780 nm. Infrared radiation (IR) is the portion of electromagnetic radiation whose wavelength is between 780 nm to 1400 nm. With high thermal efficiency, strong penetration and easy absorption, IR imaging is used extensively for communication, probing, medical and military purposes.
An optical sensor is used for converting optical signals into electrical signals using an image sensor capable of detecting light in a wavelength range of 400-1000 nm. Visible light sensors are commonly used for controlling environmental brightness. IR sensors, also called proximity sensors, are often used for surveillance purposes.
FIG. 1 illustrates the optical spectrum measured by a prior art visible light sensor. Curves R, G and B represent the transmittance-wavelength characteristics of the red, green and blue visible light, respectively. As previously explained, human eyes are unable to perceive invisible light whose wavelength is larger than 780 nm. However, the prior art visible light sensor may detect peaks in the non-visible range of the optical spectrum which results in inaccurate results. For example, when the intensity of ambient light becomes insufficient to human eyes, the prior art visible light sensor may provide an inaccurate result of sufficient ambient light due to the detection of invisible light. Therefore, optical sensors are required to simultaneously include functions of the visible light sensor and the proximity sensor in many applications.
In US Patent Application No. US 2006/0180886, a visible light sensor having a multi-layer filter structure by alternatively fabricating Ag and Si3N4 layers on an optical device is disclosed. The thickness of each layer in the multi-layer filter structure is determined according to Fabry-Perot interference principle so that each region of the optical device may detect a specific wavelength range for blocking IR light. However, this prior art requires complicated manufacturing processes which may reduce product yield or increase manufacturing costs.